Metal alkyls are valuable compounds finding extensive use in organic synthesis. They can also be used as a source of pure metal by thermo decomposition of the purified metal alkyl. For example, mixtures of gallium and arsenic alkyls can be thermally decomposed to form a gallium-arsenide alloy which in highly purified form can be used as an efficient semi-conductor.
Metal alkyls such as arsenic alkyls have been made by the reaction of aluminum alkyls with arsenic trihalides (British Pat. No. 768,765 and British Pat. No. 820,146). Trimethyl arsine has been made by the reaction of methyl magnesium iodide with arsenic trichloride (Efremov et al. "Tr. Khim. Tekhnol." 1975 (1) 3-4). A similar preparation can be made using arsenic tribromide (Berichte 39 160 (1906)). Ayscough et al. "J. Chem. Soc." 3381 (1954) report the synthesis of trimethyl arsine by reacting arsenic trichloride with methyl magnesium iodide in di-n-butyl ether.
One problem encountered in the prior methods using Grignard reagent is that the metal alkyls, especially the Group VA metal alkyls, are strong bases and coordinate with the acidic metal halides (e.g. magnesium chloride) in the reaction system making recovery difficult. This generally requires hydrolysis to remove the metal halide.
Accordingly, a need exists for an efficient method for making metal alkyls using a Grignard reagent which does not lead to complex formation of the metal alkyl with the magnesium halide by-product.